The present invention relates to an image forming apparatus, such as a copier, a printer, etc., and specifically relates to a structure of the mainframe with enhanced stiffness in the image forming apparatus.
In general, the mainframe in the image forming apparatus, is structured by two opposed vertical walls that are connected by a bottom wall and a plurality of stays. And each of the side walls, the bottom wall and the stays are structured with a single sheet of metal plate, or in necessity of high stiffness, with a rectangular pipe.
Recently, according with the requirement of high image quality, there is a tendency to structure the bottom wall support material with a rectangular pipe formed in quadrilateral shape, and under the bottom surface of the rectangular pipe are provided with casters. In this structure, there is a problem that the height of the apparatus increases excessively. In order to solve this problem, an image forming apparatus which applies flat rectangular pipes to decrease the thickness for restricting the height and maintaining the stiffness of the mainframe is disclosed in TOKKAIHEI No. 10-232525, etc.
However, even in the case of applying the flat rectangular pipe, when the apparatus is transported or moved, or affected by the flatness of the floor where the apparatus is installed, the deformation of the mainframe is concerned since the stiffness is not enough to maintain a required accuracy of the mainframe. As the result, in order to maintain the sufficient stiffness, large sized rectangular pipes need to be used, then, the height of the apparatus tends to be too large.
Overcoming the abovementioned problems in conventional image forming apparatus, it is an object of the present invention to provide an image forming apparatus, which is possible to form a high quality image by having higher stiffness than the apparatus applying the above mentioned rectangular pipes.
The object of the present invention can be achieved by the following structures.
(1) An image forming apparatus having a mainframe, which comprises two opposed vertical side walls connected to be unified with a bottom wall and at least one stay provided in the manner of leaving space from the bottom wall, wherein the bottom wall and said at least one stay are respectively have a hollow box-type structure.
(2) An image forming apparatus having a mainframe, which comprises two opposed vertical side walls connected to be unified with a bottom wall and at least one stay provided in the manner of leaving space from the bottom wall, wherein a caster for moving the image forming apparatus, is provided on the vertical side walls in such a manner that the top portion of the caster positions at higher level than the under surface of the bottom wall.